Renewing a chain

I’ve bought the XT Di2 upgrade kit and thought I’d check for chain wear, I’ve got an e-bike and have done 478 miles on the chain, I’ve  heard they wear a lot faster.

I put the chain wear tool I’ve bought into the chain and 0.75 goes into the chain after pushing it down. I’ve got a 12 speed cassette, I’ve read that you should change the chain when it goes to 0.50, when I use the tool should it just drop into the chain to get the reading?

Even though I’ve been riding Mtn bikes for at least 30 years I’ve never changed just the chain, I’ve changed it all when the gears slip.